1. Field of the Invention
The present invention relates to a wheel speed detecting device including a multi-pole magnet ring and a sensor.
2. Description of Background Art
A technique is known in which a pulsar ring is operatively connected to a wheel of a motorcycle, a detection sensor is operatively connected to a brake caliper, and a wheel speed is obtained from pulse information acquired from the pulsar ring by using the detection sensor. See, for example, FIG. 3 of Japanese Patent Application Publication No. 2006-103372.
More specifically, FIG. 3 of Japanese Patent Application Publication No. 2006-103372 illustrates the pulsar ring (32) (the number in parenthesis indicates a reference numeral described in the patent document. The same applies below) the sensor (33), and the brake caliper (31).
The pulsar ring (32) is a ring with a relatively large diameter. A technique is known in which energy loss is reduced by reducing the moment of inertia. In view of this technique, it is desirable to reduce the diameter of the pulsar ring (32).
A magnetic encoder with a reduced diameter has been proposed. See, for example, FIG. 1 of Japanese Patent Application Publication No. 2009-97997.
As shown in FIG. 1 of Japanese Patent Application Publication No. 2009-97997, a slinger (24) having a L-shaped cross section is attached to an inner ring (13) being a rotating body, and a multi-pole magnet (23) is attached to an outer side surface of the slinger (24). A movement of this multi-pole magnet (23) is detected by a rotation sensor (22) and thereby the rotation speed of the inner ring (13) can be determined.
More specifically, a wheel speed can be detected by disposing a rolling bearing (11) between an axle and a wheel of a motorcycle.
Moreover, since the multi-pole magnet (23) has a sufficiently small diameter, energy loss can be reduced.
However, in a vehicle, especially in a motorcycle, part of the muddy water splashed by a wheel sometimes enters a space between the multi-pole magnet (23) and a detecting portion (25) in FIG. 1 of Japanese Patent Application Publication No. 2009-97997. The muddy water includes various kinds of foreign objects, and the foreign objects may include iron powder which affects magnetic property.
The iron powder adheres onto the multi-pole magnet (23) by magnetic force. Thus, a countermeasure for the adhesion is demanded.
Moreover, as shown in FIG. 1 of Japanese Patent Application Publication No. 2009-97997, the rotation sensor (22) disposed outside the rolling bearing (11) is in a so-called exposed state. Thus, there is room for improvement in terms of external appearance. In addition, the rotation sensor (22) has to be supported by an unillustrated sensor stay. Here, it is inevitable for a rotation detecting device (21) including the sensor stay, the rotation sensor (22), and the multi-pole magnet (23) to become large in size. The rotation detecting device (21) is desired to have a reduced size when considered to be mounted on a motorcycle.